There are actually two of these cells on the PCB, one for the detector and one for the meter. It's simple and clever, and you can really see how it works (in fact, if you remove the LDR you can watch the LED blink in time with your input signal). Four spacers and some screws hold it together. A few off-the-shelf optocouplers exist, but, rather than use one, DIYRE designed their own discrete opto cell: an LED on the PCB is covered by a small piece of black plastic tubing, with a light-dependent resistor (LDR) on the other end of the tube. (If you'd like to learn more, there's plenty out there to read on this topic). This creates interesting, non-linear attack and release curves.

As you probably know, optical compressors work (roughly) by using audio amplitude to drive a light source, then using a light-sensitive detector to control the amount of gain reduction. The OLA5's opto cell is worth mentioning. I swapped the LM3916 chip that drives the meter and that did it a faulty part was to blame. After a few emails with DIYRE founder Peterson Goodwyn, I swapped my daughterboard with the board from the prebuilt unit I was sent. The bad news: okay, it didn't entirely work. The good news: my build worked on the first try and sounded great. My build took about five hours, including turning over records every 20 minutes (The Breeders, Cheap Trick, Heart, The Pretenders, Judas Priest, and Kiss' Alive II). As with the other DIYRE kits I've built, the parts are extremely well organized (in 14 small, numbered plastic zippered bags, which is easy to understand but seems like a lot of waste) and the build instructions are crystal clear. But it's not actually that complex вЂ“ just lots of resistors and a few caps and ICs, with a small daughterboard to drive the 10-LED meter. This kit has about 150 components, making it DIYRE's most involved kit to date.

I'm a dummy with circuits but I like building things, and soldering together a kit can be quietly therapeutic. (They also sell a 2-unit horizontal rack kit).ДIYRE sent me an assembled review unit with the 'vintage' option, and an unassembled kit to build if I chose.

One last cool feature: DIYRE sells horizontal faceplates for $15 each, in case you want a pair of side-by-side compressors in a single rack space unit. A jumper on the PCB selects the 'vintage' or op-amp-based 'modern' output stage. There's also a 'vintage' output gain option, adding an API-style discrete op-amp that feeds a custom-wound output transformer. They've also added some welcome utility features: a high-pass sidechain filter and a blend control for easy parallel compression. With the idea that the LA-4 has a superior compression detector bolted to a lackluster audio path, DIYRE used the LA-4's sidechain circuit and a newly designed signal path. They've released three or four new kits since 2015: a Colour mkII with a lot of solid improvements (I bought and built a pair) a Pultec-inspired passive EQ a Colour-loaded mic preamp and the OLA5, a 500 Series optical compressor based roughly on the Urei LA-4. I've followed DIYRE since reviewing their Colour 500 Series analog saturation platform kit, and they've been busy.

Diy 500 series preamp reviews